1. Field of the Invention
The present invention relates to a rollover determination apparatus for determining whether a vehicle will roll over (or turn over) at proper timing.
2. Description of Related Art
Conventionally, there has been provided a method of determining whether a vehicle will roll over based on a two-dimensional map of the roll angle and roll angular velocity of the vehicle, as one of the most general rollover determination techniques. In accordance with this rollover determination method, if the roll angular velocity of the vehicle is very large or rapidly increases when the vehicle accidentally has a rollover, the timing of determination of whether the vehicle will roll over becomes late. In order to solve this problem, there has been provided a method of classifying the type of the occurrence of rollover according to the acceleration of the vehicle detected by acceleration sensors (of Y-axis and/or Z-axis), and using a rollover determination threshold map suitable for the type of the occurrence of rollover. In accordance with this method, whether the vehicle will roll over is determined by using the lateral acceleration, angular velocity, and roll angle of the vehicle (refer to patent reference 1, for example).    [Patent reference 1] Japanese patent application publication (TOKKAI) No. 2,002-200,951
A problem with the prior art determination method disclosed by above-mentioned patent reference 1 is that since the method determines whether a vehicle will roll over by using the following three factors: the lateral acceleration, roll angular velocity, and roll angle of the vehicle, it is impossible to determine whether the vehicle will roll over when the lateral acceleration does not occur in coincidence with the occurrence of the roll angular velocity, or it is erroneously determined that the vehicle will roll over when such an accident as a side crash actually occurs.